The present invention pertains to processes and means for manufacturing plastic or polymeric products by introducing a deformable material into a mold chamber or cavity. Such process wherein a product is fabricated in this manner are well known in the plastics industry. Examples of such types of molding techniques include, but are not limited to: compression molding, transfer molding, injection molding, blow molding, cold molding, casting, thermo-forming and the like.
The molds employed in such molding processes generally serve two separate functions. The first function is that of shaping the material being introduced therein. The second function is that of a heat exchanger for cooling the shaped material.
It is known to those skilled in the art that a molded product, which was subjected to a uniform cooling process after being molded, is generally superior to those products which were not subjected to such a cooling process. The reason for product superiority is that, as a result of uniform cooling, the degree of internal strains and stresses within the final product are reduced, izotropically distributed, or even in some instances, completely suppressed.
Due to the temperatures employed in many typical molding processes, in order to uniformly cool a product resulting therefrom, it is generally necessary to cool the product at a very slow rate. This slow cooling rate, however, runs counter to general commercial manufacturing procedures wherein there is a continued search for means which reduce production times and/or increase production yields.
As can be seen from the above, the industry is presently plagued with a dilemma since, on the one hand, there is a desirability to produce molded plastic products with superior properties and, on the other hand, there is a desirability to reduce production times (i.e., increase production yields). In other words, since quickly cooling the molded material can result in localized hot spots which, in turn, create internal strains and stresses within the product, a skilled artisan would be inclined to slowly and uniformly cool the molded product. However, since it is equally desirable to increase production yields, the same skilled artisan would have a similar inclination to rapidly cool the molded product. In view of this dilemma, the plastics industry must sometimes sacrifice product quality in favor of reduced production times and/or vice versa.
If a means can be devised which can produce a molded product with a lesser degree of internal strains and stresses, without significantly increasing production times, it would be a welcomed improvement in the plastics industry.
It is known in the industry that rheological properties of a plastic or polymeric material can be controlled and/or altered by subjecting the material to a process wherein the temperature of the material is simultaneously varied with at least one other rheological variable such as hydrostatic pressure, shear stress, mechanical vibration (frequency or amplitude), dielectric vibration (frequency or amplitude) for dielectric materials and/or electromagnetic properties for metallic materials. The variation in temperature and the simultaneous variation in one or more other rheological variables are intimately connected by a relationship selected and specifically programmed to obtain a product having improved properties. An example of such a process is disclosed in U.S. Pat. No. 4,469,649 which is incorporated herein by reference.
As used herein, the phrase "rheological transformation", as it pertains to a process or stage, generally refers to a process/stage wherein at least one of the rheological properties of a material are controlled and/or altered by subjecting the material to vibrations (e.g., mechanical or electrical) as set out above.
In conventional practices where such rheological transformation processes are employed in conjunction with a molding process, the mold containing the molded material typically remains at the site where the material was introduced into the mold (e.g., the injection site of an injection molding process) as the material receives the vibrational treatment. This practice, however, results in a significant amount of vibrational energy being lost to structures other than the material within the mold.
Due to this significant loss and/or misdirection of vibrational energy, conventional molding processes which employ such a rheological transformation stage are generally limited to the treatment of very small products (e.g., candy boxes, electrical plugs, etc.). In these circumstances, although a significant amount of vibrational energy is lost or misdirected, there is still significant levels of vibration communicated to the material within the mold.
If a means can be devised wherein a material can be efficiently subjected to a rheological transformation process as described above, regardless of the molded material's size, it would be a welcomed improvement in the plastics industry due to the many advantages associated with such rheological transformation processes.